Food Biochemistry and Food Processing (2 edition)

BLBS102-c09 BLBS102-Simpson March 21, 2012 11:15 Trim: 276mm X 219mm Printer Name: Yet to Come

9 Enzymes in Food Processing 191

oryzaeknown as asperzyme and a liquid saccharifying amylase

for the production of fermentable sugars known as adjuzyme,

which is derived fromA. niger. An Enzeco glucoamylase powder

derived fromA. nigeris also commercially available for use in

baked goods to improve proofing in lean or frozen doughs, and

brewers amylase produced in powder form fromAspergillus

spandRhizopus oryzaeis used for the manufacture of light

beers. Others are Brewers Fermex derived fromAspergillus sp.

andRhizopus oryzaein powder form for use in increasing the

fermentability of wort and cookerzyme derived fromB. subtilis

for accelerated hydrolysis of starch adjuncts.

Galactosidases and Lactases

Galactosidases are those carbohydrases that catalyze the

hydrolysis of galactosides such as lactose, lactosylceramides,

ganglioside, and various glycoproteins into their constituent

monosaccharide units. Two types of galactosidases are

distinguished based on their mode of action asα-andβ-

galactosidases. Theα-galactosidases (also known asα-gal)

catalyze the hydrolytic cleavage of the terminalα-galactosyl

residues fromα-galactosides (including certain glycoproteins

and glycolipids) and they can catalyze the hydrolysis of the

disaccharide melibiose into galactose and glucose.α-Gal is used

as a dietary supplement (e.g., beano) to facilitate the breakdown

of complex sugars into simpler forms to permit easier digestion

and reduce intestinal gas and bloating. The enzyme may also be

used to reduce the complex carbohydrate content of the beer to

increase the simple sugar content and hence the alcohol content

of beer. Theβ-gals facilitate the hydrolysis ofβ-galactosides

such as lactose, various glycoproteins, and ceramides into

simpler forms.

Lactases belong to theβ-galactosidase family of enzymes;

they catalyze the breakdown of the milk sugar lactose into

its constituent monosaccharides, galactose and glucose units,

that is,

Lactose+H 2 O⇔Galactose+Glucose

Lactases are produced in commercial quantities from yeasts

such asK. fragilisandK. lactis,and from fungi such asA. niger

andA. oryza(Mustranta et al. 1981). Other lactase-producing

microorganisms include the bacteriaStreptococcus cremoris,

Lactobacillus bulgaricus,andLeuconostoc citrovorum(Ramana

Rao and Dutta 1978). Lactases are also found in the mucous

lining of the small intestines of cows and rabbits, and in the

walls of the small intestines of humans from as early as the

fifth month of intrauterine life. However, lactase levels tend to

be higher in younger animals and human infants, and the levels

generally decrease with age (Heilskov 1951). The enzyme is

also found in plants, e.g., from the calli and roots of gherkin,

pea, poppy, and eastern blue star seedlings (Neubert et al. 2004).

Lactase is commercially produced by Novozymes from the

dairy yeastK. lactisand marketed as Lactozym. Lactase as lac-

tozym is widely used in the dairy industry to produce fermented

milks, ice-cream, milk drinks, and lactose-reduced milk for peo-

ple who are lactose-intolerant and for household pets (e.g., cats)

that cannot utilize lactose. Milks treated with lactose tend to be

sweeter than their untreated counterparts because the monosac-

charides glucose and galactose produced in the treated milks are

sweeter than the disaccharide lactose in untreated milks. Crys-

tallization of lactose in condensed milk can also be prevented by

treating the milk first with lactase. Lactase-treated milks used for

the preparation of cultured milk products (e.g., cottage cheese

or yogurt) ferment faster than untreated milks, because lactose

in the latter ferment at a slower pace than the glucose and galac-

tose in the treated milks. As well, the cultured milk products

from the lactase-treated milks tend to be sweeter than the prod-

ucts prepared from the nontreated milks. Milk whey may also

be treated with lactase and concentrated to form syrups for use

as a sweetener in food products. Ice cream made from lactase-

treated milk (or whey) also has little or no lactose crystals, thus

the undesirable “sandy” feel due to lactose crystallization is

averted.

Maltases

Maltase is the carbohydrase that breaks down the disaccharide

maltose into glucose units as summarized in the reaction below:

Maltose+H 2 O⇔ 2 α-Glucose

Maltase is found in humans and other vertebrate animals,

plants, and microorganisms (bacteria and yeast). In humans,

digestion of starch commences in the mouth with ptyalin (saliva

enzyme) and pancreatic amylases breaking down the starch into

maltose. The maltose is subsequently hydrolyzed by intestinal

maltase into glucose for utilization by the body to produce energy

or for storage in the liver as glycogen. Maltase (from barley malt)

is used in brewing to increase the glucose content for conversion

into alcohol. Maltase fromA. oryzaeis used in the beet-sugar and

molasses distilleries, and in the industrial production of glucose

syrups (McWethy and Hartman 1979).

Cellulases

Cellulases are enzymes that potentiate the breakdown of theβ-

1,4-glycosidic bonds in cellulose. They are produced commonly

by bacteria (e.g., Clostridium thermocellum, Acidothermus

cellulolyticus(Tucker et al. 1988)), fungi (Trichoderma reesei,

T. hamatum,Fusarium roseum,Curvularia lunata(Sidhu et al.

1986)), and protozoa (e.g.,Trichomitopsis termopsidis(Odelson

and Breznak 1985),Eudiplodinium maggii, Epidinium ecauda-

tum caudatum,andOstracodinium obtusum bilobum(Coleman

1985)), although the enzymes are also found in plants (e.g., cress

and pepper (Ferrarese et al. 29)) and animals (e.g., termites, crus-

tacea, insects, and nematodes (Watanabe and Tokuda 2001)). A

simplified equation for the hydrolysis of cellulose by cellulases

may be summarized as

Cellulose+H 2 O⇔nβ-D-Glucose

Native cellulose is highly crystalline in nature and its com-

plete hydrolysis entails stepwise reactions catalyzed by a com-

plex of cellulase enzymes. It entails the preliminary unraveling

of the crystalline cellulose molecules into simple (or linear)

cellulose chains by endocellulases. The linear cellulose chains